fix: embed images inline in Gitea issues, fix retry dropping attachments (v0.51.6)

Two related bugs in the Gitea issue body:

1. Attachments were always plain bullet links (`- url`), even for images —
   so they never rendered as a preview in the Gitea issue, just a clickable
   URL. Image content-types now use markdown image embed (`![](url)`).
2. The admin "Create Gitea issue" retry action built its own body from
   scratch (`ticket.description` only) and never queried attachments at
   all — a retry always lost them, regardless of point 1's fix.

Extracted buildGiteaIssueBody() to lib/gitea.ts so both the initial
ticket-creation path and the retry path share one body-building
implementation instead of two independent (and inevitably diverging) ones.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/lib/changelog.ts

@@ -1,5 +1,5 @@
 // Mirrors CHANGELOG.md at the repo root — update both together.
-export const APP_VERSION = "0.51.5";
+export const APP_VERSION = "0.51.6";
 
 export type ChangelogEntry = {
   version: string;
@@ -11,6 +11,13 @@ export type ChangelogEntry = {
 };
 
 export const CHANGELOG: ChangelogEntry[] = [
+  {
+    version: "0.51.6",
+    date: "2026-07-19 13:20",
+    fixed: [
+      "Image attachments on support tickets now embed inline in the Gitea issue (rendered preview) instead of just a plain link. Also fixed the admin \"Create Gitea issue\" retry action, which was dropping attachments entirely and only ever sent the ticket description.",
+    ],
+  },
   {
     version: "0.51.5",
     date: "2026-07-19 13:05",